Fuel injection amount control system for internal combustion engine

ABSTRACT

A fuel transportation lag model has a fuel transportation lag element A (FTLEA) due to adhesion of an injected fuel onto wall faces and a first-order lag element B (FOLEB) for compensating a model error of the (FTLEA). A fuel correction amount has a (FTLEA) compensation term and a (FOLEB) compensation term. By a compensation term for the (FTLEA), a first wall adhesion correction amount is obtained by multiplying a deviation between the wall face adhesion fuel amount (WFAFA) in a steady driving mode and a (WFAFA) at a present time with a first reference adaptation parameter and a first correction factor. By a compensation term for the (FOLEB), a second wall adhesion correction amount is obtained by multiplying a deviation between a required fuel amount of a present time and a required fuel amount of last time with a second reference adaptation parameter and a second correction factor.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is based on and incorporates herein by referenceJapanese Patent Application No. 2001-27813 filed on Feb. 5, 2001.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention:

[0003] The present invention relates to a fuel injection control systemfor an internal combustion engine. More specifically, the inventionrelates to a fuel injection system for compensating fuel transportationlag, of a fuel transportation system, which transports fuel injectedfrom a fuel injection valve to a cylinder of an internal combustionengine.

[0004] 2. Related Background Art:

[0005] In many gasoline engines mounted on vehicles, a fuel injectionvalve is attached to an intake pipe and fuel (gasoline) is injected toan intake port. In the intake port injection of fuel, some of the fuelinjected from the fuel injection valve is directly taken into acylinder, but the rest of the fuel is adhered to the internal wall andassociated parts of the intake port, and after that, the fuel graduallyevaporates and is drawn into the cylinder. As an equation of modelingthe behavior of the fuel in such a fuel transport system, the followingAquino equation is known:

MF(t)=(1−Δt/τ)·MF(t−Δt)+X·GF(t−Δt)

[0006] where MF(t) is an amount of fuel adhered to the wall face at thepresent time t, Δt is an operation cycle, τ is a fuel vaporization timeconstant, MF(t−Δt) is an amount of fuel adhered to the wall face at thetime of operation of last time, X is a fuel adhesion rate, and GF(t−Δt)is a fuel injection amount at the time of operation of last time.

[0007] In JP-A No. 8-177556, it is proposed to calculate the fuelinjection amount GF(t) by the following equation by using the amount MFof the fuel adhered to the wall face calculated by the above equation.GF(t) is calculated as follows:

GF(t)=GFET/(1−Aα)−Aα·MF(t−Δt)

[0008] where GFET is a required fuel amount, and Aα is obtained bysequentially multiplying an Aquino operator α (=1−Δt/τ) calculated everysampling as shown by the following equation:

Aα=α(t)·α(t−Δt)·α(t−2Δt)·. . . ·α(t−nΔt)

[0009] In the fuel injection amount controlling method of thepublication, each physical parameter such as the fuel vaporization timeconstant τ, wall face adhesion rate X, and Aα must be calculated usingan arithmetic expression, a map, and/or the like. Consequently, the loadon the CPU is high and the number of physical parameters to becalculated is large. This means that a number of adapting steps isrequired when the method is applied to an actual vehicle, and highdevelopment costs are a drawback.

SUMMARY OF THE INVENTION

[0010] At least one embodiment of the invention has been achieved inconsideration of such circumstances and its object is to provide a fuelinjection amount control system for an internal combustion engine.Further, the system will realize low development costs and facilitateactual adaptation of the system to a vehicle and also reduce a load onthe CPU.

[0011] In order to achieve the object, according to at least oneembodiment of the invention, there is provided a fuel injection amountcontrol system for an internal combustion engine. The system compensatesfor a fuel transportation lag by using a fuel transportation lag modelobtained by modeling a fuel transportation lag of a fuel transportationsystem that transports fuel injected from a fuel injection valve into acylinder and associated intake system within an internal combustionengine. Additionally, physical parameters such as a fuel vaporizationtime constant, a wall face adhesion rate of an injected fuel, and thelike are included in the fuel transportation lag model and converted toa small number of adaptation parameters. With such a configuration, thenumber of parameters to be computed is reduced, so that the number ofadaptation steps for adapting the system to an actual vehicle,development costs, and the load on a CPU can all be reduced.

[0012] It is also possible to construct the adaptation parameters by areference adaptation parameter and a correction factor, use a systemidentification value or a physical measurement value as the referenceadaptation parameter, and correct a wall face adhesion correction amountobtained by using the reference adaptation parameter by the correctionfactor. For example, by adapting the correction factor in accordancewith fluctuation of an air-fuel ratio, the fluctuation in the air-fuelratio can be converged with a high response.

[0013] The fuel transportation lag model may contain a configurationsuch that a fuel transportation lag element A, due to adhesion of theinjected fuel onto the wall face, and a first-order lag element B, forcompensating a model error of the fuel transportation lag element A, arecoupled in series. Fluctuations in the air-fuel ratio at the time ofacceleration/deceleration are caused not only by the fuel transportationlag due to the adhesion of the injected fuel to the wall face, but alsofactors such as an error in measurement (estimation) of an air volumecharged in a cylinder. The error in measurement (estimation) of thecylinder charging air volume can be approximated by the first-order lagof the fuel transportation lag. Consequently, by coupling thefirst-order lag element B to the fuel transportation lag element A inseries, the model error due to the error in measurement (estimation) ofthe cylinder charging air volume or the like can be compensated, so thataccuracy in computing the fuel correction amount can be improved.

[0014] An equation for computing a fuel correction amount by using thefuel transportation lag model may be constructed using a compensationterm for the fuel transportation lag element A and a compensation termfor the first-order lag element B. With the configuration, thecomputation equation of the fuel correction amount is simplified to twocompensation terms. It further facilitates the adaptation to an actualvehicle.

[0015] In this case, in a compensation term for the fuel transportationlag, a first wall face adhesion correction amount may be obtained. Thisis done by multiplying a deviation between the wall face adhesion fuelamount in a steady driving mode and a wall face adhesion fuel amount ata present time, a deviation between a present intake manifold pressureand a smoothed intake manifold pressure, or a deviation between apresent intake air volume and a smoothed intake air volume with a firstreference adaptation parameter and a first correction factor. With theconfiguration, the first wall face adhesion correction amount forcompensating the fuel transportation lag can be computed with a highdegree of accuracy by a simple arithmetic operation.

[0016] Duration of the first wall face adhesion correction amount may beexpressed by a function of the fuel vaporization time constant. Thus,the duration of the first wall face adhesion correction amount can beproperly set in accordance with the evaporation characteristics of thefuel adhered on the wall face.

[0017] In a compensation term for the first-order lag element B, asecond wall adhesion correction amount may be obtained in two ways.First, by multiplying a deviation between a required fuel amount of thepresent time and a required fuel amount of the previous time, orsecondly, by multiplying a deviation between an intake manifold pressureof this time and an intake manifold pressure of last time, with a secondreference adaptation parameter and a second correction factor. With theconfiguration, the second wall face adhesion correction amount forabsorbing the model error can be accurately computed.

[0018] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiment of the invention,are intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The invention, together with additional objectives, features andadvantages thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings in which:

[0020]FIG. 1 is a schematic configuration diagram of an entire enginecontrol system as a first embodiment of the invention;

[0021]FIG. 2 is a flowchart showing the flow processes of a fuelcorrection amount computing program;

[0022]FIG. 3 is a block diagram schematically showing a system forcompensating a fuel transportation lag;

[0023]FIG. 4 is a block diagram showing a first embodiment of a fueltransportation lag model;

[0024]FIG. 5 is a block diagram showing a fuel transportation lag modelof a second embodiment; and

[0025]FIG. 6 is a block diagram showing a fuel transportation lag modelof a third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The following description of preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses.

[0027] A first embodiment of the invention will be described below withreference to FIGS. 1 through 4. First, the schematic configuration of anentire engine control system will be described by referring to FIG. 1.In the uppermost stream portion of an intake pipe 12 of internalcombustion engine 11, an air cleaner 13 is provided. On the downstreamside of the air cleaner 13, an air flow meter 14 for detecting an intakeair volume is provided. On the downstream side of the air flow meter 14,a throttle valve 15 and a throttle angle sensor 16, for sensing athrottle angle, are provided. A surge tank 17 is provided downstream ofthe throttle valve 15, and the surge tank 17 is provided with an intakemanifold pressure sensor 18 for sensing an intake manifold pressure Pm.The surge tank 17 is also provided with an intake manifold 19 forintroducing air into all cylinders of the internal combustion engine 11.A fuel injection valve 20, for injecting fuel, is attached near theintake port of the intake manifold 19 of each cylinder.

[0028] At some point within the length of an exhaust pipe 21 of theengine 11, a catalyst 22 is disposed. The catalyst 22 may be a three-waycatalyst for reducing CO, HC, NOx, and the like, in an exhaust gas. Onthe upstream side of the catalyst 22, an air-fuel ratio sensor 23 isprovided for sensing the air-fuel ratio or a rich/lean state of theexhaust gas. To a cylinder block of the engine 11, a cooling watertemperature sensor 24 for sensing a cooling water temperature Thw and acrank angle sensor 25 for sensing engine speed Ne are attached.

[0029] Outputs of the sensors are input to an engine control unit(described below as “ECU”) 26. The ECU 26 is constructed by using amicrocomputer as a main body. The ECU 26 calculates a fuel correctionamount WETC for compensating a fuel transportation lag of a fueltransportation system. The fuel transportation system transports thefuel injected from the fuel injection valve 20 to each cylinder byexecuting a fuel correction amount computing program of FIG. 2 stored ina built-in ROM (storage medium). A required fuel amount GFET iscorrected by the fuel correction amount WETC, thereby obtaining a finalfuel injection amount GF (injection time). Fuel injection is executed byapplying an injection signal having a pulse width according to the fuelinjection amount GF to the fuel injection valve 20 at the time of eachinjection.

[0030] A method of computing the fuel correction amount WETC from thefuel transportation lag model will now be described by referring to FIG.3. The fuel transportation lag model has a configuration such that afuel transportation lag element A, due to adhesion of the injected fuelon the wall face of the intake port and associated parts, and afirst-order lag element B, for compensating a model error of the fueltransportation lag element A, are coupled in series. Fluctuations in theair-fuel ratio at the time of acceleration/deceleration are caused notonly by the fuel transportation lag due to the adhesion of the injectedfuel to the wall face, but also by factors such as an error inmeasurement (estimation) of an air volume charged in a cylinder. Theerror in measurement (estimation) of the cylinder charging air volumecan be approximated by the first-order lag of the fuel transportationlag. Consequently, as shown in FIGS. 3 and 4, by coupling thefirst-order lag element B to the fuel transportation lag element A, inseries, the model error due to the error in measurement (estimation) ofthe cylinder charging air volume or the like can be compensated, so thatthe accuracy in calculating the fuel correction amount WETC can beimproved.

[0031] The fuel transportation lag element A is expressed by thefollowing Aquino equation:

MF(t)=(1−Δt/τ)·MF(t−Δt)+X·GF(t−Δt)

[0032] where MF(t) is an amount of fuel adhered to the wall face at thepresent time t, Δt is an operation cycle, τ is a fuel vaporization timeconstant, MF(t−Δt) is an amount of fuel adhered to the wall face at thetime of operation of last time, X is a fuel adhesion rate, and GF(t−Δt)is a fuel injection amount of operation of last time.

[0033] A fuel amount Gcy′ (an output of the fuel transportation lagelement A) drawn into a cylinder, which is calculated from Aquino'sequation, is expressed by the following equation:

Gcy′=(1−X)·GF+(1−a)·MF  (1)

[0034] where “a” is a fuel residual rate, a−1−Δt/τ,(1−X)·GF denotes anamount of fuel which is directly drawn into a cylinder without beingadhered to the wall face, and (1−a)·MF is an amount of fuel whichevaporates from the wall face and is drawn into the cylinder.

[0035] The amount Gcy of fuel taken into the cylinder after model errorcompensation (output of the first-order lag element B) is expressed bythe following equation:

Gcy=Gcy′+a ₂ {Gcy(t−Δt)−Gcy′}  (2)

[0036] where a₂=1−Δt/τ₂ (τ₂ is a time constant of the first-order lagelement B)

[0037] When the equation (1) is substituted into equation (2), thefollowing equation is derived:

Gcy=(1−X)·GF·(1−a ₂)+(1−a)·MF·(1−a ₂)+a ₂ ·Gcy(t−Δt)  (3)

[0038] When Gcy=GFET and Gcy(t−Δt)=GFET(t−66 t), the following equationis obtained.

[0039] [Equation 1] $\begin{matrix}{{G\quad F} = {\frac{G\quad F\quad E\quad T}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} - {{\frac{1 - a}{1 - X} \cdot M}\quad F} - {{\frac{a_{2}}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} \cdot G}\quad F\quad E\quad {T\left( {t - {\Delta \quad t}} \right)}}}} & (4)\end{matrix}$

[0040] The final fuel injection amount GF is calculated by adding thefuel correction amount WETC to the required fuel amount GFET.

GF=GFET+WETC  (5)

[0041] When the equation (5) is substituted for GF in equation (4) tosolve for the fuel correction amount WETC, the following equation isobtained:

[0042] [Equation 2] $\begin{matrix}\begin{matrix}{{W\quad E\quad T\quad C} = {{{\left\{ {\frac{1}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} - 1} \right\} \cdot G}\quad F\quad E\quad T} - {{\frac{1 - a}{1 - X} \cdot M}\quad F} - {{\frac{a_{2}}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} \cdot G}\quad F\quad E\quad {T\left( {t - {\Delta \quad t}} \right)}}}} \\{= {\frac{X}{1 - X} + {{\frac{a_{2}}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} \cdot G}\quad F\quad E\quad T} - {{\frac{1 - a}{1 - X} \cdot M}\quad F} - {{\frac{a_{2}}{\left( {1 - X} \right)\left( {1 - a_{2}} \right)} \cdot G}\quad F\quad E\quad {T\left( {t - {\Delta \quad t}} \right)}}}} \\{= {{\frac{1 - a}{1 - X} \cdot \left( {{M\quad F\quad s\quad t\quad a\quad b\quad l\quad e} - {M\quad F}} \right)} + {\frac{1}{1 - X} \cdot \frac{a_{2}}{1 - a_{2}} \cdot \left\{ {{G\quad F\quad E\quad T} - {G\quad F\quad E\quad {T\left( {t - {\Delta \quad t}} \right)}}} \right\}}}}\end{matrix} & (6)\end{matrix}$

[0043] where, MFstable denotes a cylinder wall face adhered fuel amountwhich is an amount of fuel stably adhered to the inner wall face of theintake system in a steady driving mode. In the steady driving mode,MF(t)=MF(t−Δt)=MFstable, GF(t)=GF(t−Δt), and Gcy′=Gcy=Gy. Consequently,the following equation is obtained from equation (1).

[0044] [Equation 3] $\begin{matrix}{{M\quad F\quad s\quad t\quad a\quad b\quad l\quad e} = {{\frac{X}{1 - a} \cdot G}\quad F}} & (7)\end{matrix}$

[0045] When the parameter (1−a)/(1−X) in the first term of the equation(6) is set as a first reference adaptation parameter b₁ and theparameter 1/(1−X)·,a₂/(1−a ₂) is set as a second reference adaptationparameter b₂, the fuel correction amount WETC is calculated by thefollowing equation.

WETC=b ₁·(MFstable−MF)+b ₂ ·{GFET−GFET(t−Δt)}  (8)

[0046] In the above equation, b₁·(MFstable−MF) of the first term is acompensation term for the fuel transportation lag element A (calculationterm of the first wall face adhesion correction amount), andb₂·{GFET−GFET(t−Δt)} of the second term is a compensation term(calculation term of the second wall face adhesion correction amount)for the first-order lag element B. Further, in order to facilitateadaptation to an actual vehicle, it is sufficient to calculate the fuelcorrection amount WETC by the following equation in which the first andsecond terms are multiplied by a first correction factor k₁ and a secondcorrection factor K₂, respectively, as shown in:

WETC=b ₁ ·k ₁·(MFstable−MF)+b ₂ ·k ₂ ·{GFET−GFET(t−Δt)}  (9 )

[0047] By the above equation, the first wall face adhesion correctionamount is obtained by multiplying the deviation between the wall faceadhesion fuel amount MFstable in the steady driving mode and the wallface adhesion fuel amount MF at the present time by the first referenceadaptation parameter b₁ and the first correction factor k₁. Duration ofthe first wall face adhesion correction amount may be expressed by afunction of the fuel evaporation time constant τ. The second wall faceadhesion correction amount is obtained by multiplying the deviationbetween the required fuel amount GFET of this time and the required fuelamount GFET(t−Δt) of the last time by the second reference adaptationparameter b₂ and the second correction factor k₂.

[0048] The adaptation parameters (reference adaptation parameters b₁ andb₂ and correction factors k₁ and k₂) may be adapted by one of thefollowing methods (a) and (b).

[0049] (a) By setting each of the correction factors k₁ and k₂ to 1, thereference adaptation parameters b₁ and b₂ are adapted from a map or thelike in accordance with the fluctuations in the air-fuel ratio.

[0050] (b) By using a system identification value or a physicalmeasurement value as each of the reference adaptation parameters b₁ andb₂ the correction factors k₁ and k₂ are adapted from a map or the likein accordance with fluctuations in the air-fuel ratio.

[0051] The details of the processes of the fuel correction amountcomputing program of FIG. 2 will now be described. The program isexecuted periodically and synchronously with an injection timing of eachcylinder. When the program is started, first, in step 101, the enginespeed Ne, intake manifold pressure Pm, and cooling water temperature Thw(temperature information in place of the wall face temperature of theintake manifold 19) detected by the sensors 25, 18, and 24,respectively, are read. In step 102, the required fuel amount GFET iscalculated by the following equation:

GFET=basic injection amount×air-fuel ratio learn value ×(after-startincrease amount factor +OTP increase amount factor)

[0052] where required fuel amount GFET is an amount of fuel to be drawninto the cylinder in the steady driving mode. The basic injection amountis obtained from a map or the like in accordance with engine operationparameters such as the engine speed Ne and intake manifold pressure Pm.The air-fuel ratio learn value is a learn value for correcting adeviation of the air-fuel ratio due to a change in time or the like. Theafter-start increase amount factor is a fuel correction factor forcorrecting cylinder wetting which occurs immediately after starting andthe like, and the OTP increase amount factor is a fuel correction factorfor correcting the injection amount so as to be increased to protect thecatalyst 22 and the like at the time of high load.

[0053] After computing the required fuel amount GFET, the programadvances to step 103 where model parameters a, X, and a₂ of the fueltransportation lag model are calculated by the following equations usingtwo-dimensional maps map11 through map32:

a=map11(Ne,Pm)×map12(Ne,Thw)

X=map21(Ne,Pm)×map22(Ne,Thw)

a ₂=map31(Ne,Pm)×map32(Ne,Thw)

[0054] where, each of map11(Ne, Pm), map21(Ne, Pm), and map31(Ne, Pm) isa two-dimensional map using the engine speed Ne and the intake manifoldpressure Pm as variables, and each of map12(Ne, Thw), map22(Ne, Thw),and map32(Ne, Thw) is a two-dimensional map using the engine speed Neand the cooling water temperature Thw as variables. In this case,a=1−Δt/τ (where τ denotes a fuel vaporization time constant) anda₂=1−Δt/τ₂ (where τ₂ is a time constant of the first-order lag elementB).

[0055] In this case, in order to satisfy the relation that the wall faceadhesion fuel amount MFstable in the steady driving mode is almostproportional to the intake manifold pressure Pm and hardly changes withthe engine speed Ne also in the case where the wall face temperature(cooling water temperature Thw) of the intake manifold 19 is low, thecorrection term by the wall face temperature (cooling water temperatureThw) has to be made variable also with the engine speed Ne. For thispurpose, in the first embodiment, the correction term by the wall facetemperature (cooling water temperature Thw) is calculated fromtwo-dimensional maps map12(Ne, Thw), map22(Ne, Thw), and map32(Ne, Thw)using the engine speed Ne and the cooling water temperature Thw asvariables.

[0056] After computing the model parameters a, X, and a₂, the programadvances to step 104 where the wall face adhesion fuel amount MF iscalculated by the following equation:

MF(t)=(1−t/τ)·MF(t−Δt)+X·GF(t−Δt)

[0057] where MF(t) is an amount of fuel adhered to the wall face at atime t, Δt is an operation period (for example, interval of injectionsof each cylinder), τ is fuel vaporization time constant, MF(t−Δt) is anamount of fuel adhered to the wall face at the time of operation of lasttime, and GF(t−Δt) is a fuel injection amount of operation of last time.When the operation cycle At is set to an injection interval (720° CA) ofeach cylinder, MF(t−Δt) is a wall face adhesion fuel amount before 720°CA, and GA(t−Δt) is a fuel injection amount before 720° CA.

[0058] After that, the program advances to step 105 where the adaptationparameters (reference adaptation parameters b₁ and b₂ and correctionfactors k₁ and k₂) are adapted by any of the following methods (a) and(b).

[0059] (a) By setting each of the correction factors k₁ and k₂ to 1, thereference adaptation parameters b₁, and b₂ are adapted from a map or thelike in accordance with a fluctuation in the air-fuel ratio.

[0060] (b) By using a system identification value or a physicalmeasurement value as each of the reference adaptation parameters b₁ andb₂, the correction factors k₁ and k₂ are adapted from a map or the likein accordance with a fluctuation in the air-fuel ratio.

[0061] After that, the program advances to step 106 where the fuelcorrection amount WETC is calculated by the following equation using thereference adaptation parameters b₁ and b₂ and correction factors k₁ andk₂.

WETC=b ₁ ·k ₁·(MFstable−MF)+b ₂ ·k ₂ ·{GFET−GFET(t−Δt)}

[0062] According to the foregoing first embodiment, the fuel correctionamount WETC can be calculated by the small number of adaptationparameters (reference adaptation parameters b₁ and b₂ and correctionfactors k₁ and k₂) and the number of adaptation steps for adapting thesystem to an actual vehicle can be made small. Therefore, a lowdevelopment cost can be achieved, the operating process can besimplified, and the load on the CPU can also be reduced.

[0063] In the first embodiment, in the compensation term for the fueltransportation lag element A, the first wall face adhesion correctionamount is obtained by multiplying the deviation between the wall faceadhesion fuel amount MFstable in the steady driving mode and the wallface adhesion fuel amount MF at a present time by the first referenceadaptation parameter b₁ and the first correction factor k₁. However, inplace of the deviation between the wall face adhesion fuel amountMFstable in the steady driving mode and the wall face adhesion fuelamount MF at a present time, a deviation between a present intakemanifold pressure and a smoothed intake manifold pressure (obtained bylagging the intake manifold pressure by the fuel vaporization timeconstant τ so as to have a first-order lag), or a deviation between apresent intake air volume and a smoothed intake air volume (obtained bylagging the intake air volume by the fuel vaporization time constant τso as to have a first-order lag) may be used.

[0064] In the first embodiment, in the compensation term for thefirst-order lag element B, the second wall face adhesion correctionamount is obtained by multiplying the deviation between the requiredfuel amount GFET of a present time and the required fuel amountGFET(t−Δt) of last time by the second reference adaptation parameter b₂and the second correction factor k₂. However, in place of the deviationbetween the required fuel amount GFET of a present time and the requiredfuel amount GFET(t−Δt) of last time, a deviation between an intakemanifold pressure of this time and an intake manifold pressure of lasttime may be used.

[0065] The operation cycle Δt is not limited to the injection interval(720° CA) of each cylinder but may be set to a cycle other than theinjection interval.

[0066] In a second embodiment of a fuel transportation lag model of FIG.5, the relation between the wall face adhesion fuel amount MFstable inthe steady driving mode and the required fuel amount GFET isapproximated by the following equation: $\begin{matrix}\begin{matrix}{\left\lbrack {{Equation}\quad 4} \right\rbrack \quad} \\{{M\quad F\quad s\quad t\quad a\quad b\quad l\quad e} = {{\frac{X}{1 - a} \cdot G}\quad F\quad E\quad T}}\end{matrix} & (7)\end{matrix}$

[0067] GFET in the above equation is approximate to GF in Equation 7.

[0068] The wall face adhesion fuel amount MF at a present time isobtained by lagging the wall face adhesion fuel amount MFstable in thesteady driving mode by the fuel vaporization time constant τ so as tohave a first-order lag. By multiplying the deviation between the wallface adhesion fuel amount MFstable in the steady driving mode and thewall face adhesion fuel amount MF at the present time by the firstreference adaptation parameter b1=(1−a)/(1−X), the first wall faceadhesion correction amount equals (MFstable−MF)×b₁.

[0069] In a third embodiment, a fuel transportation lag model of FIG. 6is obtained by multiplying the first reference adaptation parameter b₁,with the parameter X/(1−a) for converting the required fuel amount GFETinto the wall face adhesion fuel amount MFstable in the steady drivingmode so that the parameters are integrated to a single adaptationparameter X/(1−X). Therefore, in the fuel transportation lag mode ofFIG. 6, the deviation between the required fuel amount GFET and thevalue GFET′, obtained by lagging the required fuel amount GFET by thefuel vaporization time constant τ so as to have a first-order lag, ismultiplied by the adaptation parameter X/(1−X), thereby obtaining thefirst wall face adhesion correction amount equal to(GFET−GFET′)·X/(1−X).

[0070] The description of the invention is merely exemplary in natureand, thus, variations that do not depart from the gist of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A fuel injection amount control system for aninternal combustion engine, comprising a compensation term forcompensating a fuel transportation lag by using a fuel transportationlag model obtained by modeling a fuel transportation lag of a fueltransportation system for transporting a fuel injected from a fuelinjection valve into an intake system so as to be taken into a cylinderof an internal combustion engine, wherein physical parameters such as afuel vaporization time constant and a wall face adhesion rate of aninjected fuel, included in the fuel transportation lag model, areconverted to adaptation parameters.
 2. The fuel injection amount controlsystem for an internal combustion engine according to claim 1, whereinthe adaptation parameters include a reference adaptation parameter and acorrection factor, and either a system identification value or aphysical measurement value is used as the reference adaptationparameter, and a wall face adhesion correction amount, obtained by usingthe reference adaptation parameter, is corrected by the correctionfactor.
 3. The fuel injection amount control system for an internalcombustion engine according to claim 1, wherein the fuel transportationlag model has a configuration that a fuel transportation lag element Adue to adhesion of the injected fuel onto the wall face and afirst-order lag element B, for compensating a model error of the fueltransportation lag element A, are coupled in series.
 4. The fuelinjection amount control system for an internal combustion engineaccording to claim 2, wherein the fuel transportation lag model has aconfiguration that a fuel transportation lag element A due to adhesionof the injected fuel onto the wall face and a first-order lag element B,for compensating a model error of the fuel transportation lag element A,are coupled in series.
 5. The fuel injection amount control system foran internal combustion engine according to claim 3, wherein an equationfor computing a fuel correction amount by using the fuel transportationlag model includes a compensation term for the fuel transportation lagelement A and a compensation term for the first-order lag element B. 6.The fuel injection amount control system for an internal combustionengine according to claim 4, wherein an equation for computing a fuelcorrection amount by using the fuel transportation lag model includes acompensation term for the fuel transportation lag element A and acompensation term for the first-order lag element B.
 7. The fuelinjection amount control system for an internal combustion engineaccording to claim 1, wherein in a compensation term for the fueltransportation lag, a first wall face adhesion correction amount isobtained by multiplying a deviation between a wall face adhesion fuelamount in a steady driving mode and a wall face adhesion fuel amount ata present time, a deviation between a present intake manifold pressureand a smoothed intake manifold pressure, or a deviation between apresent intake air volume and a smoothed intake air volume with a firstreference adaptation parameter and a first correction factor.
 8. Thefuel injection amount control system for an internal combustion engineaccording to claim 7, wherein duration of the first wall face adhesioncorrection amount is expressed by a function of the fuel vaporizationtime constant.
 9. The fuel injection amount control system for aninternal combustion engine according to claim 5, wherein in acompensation term for the first-order lag element B, a second walladhesion correction amount is obtained by multiplying a deviationbetween a required fuel amount of a present time and a required fuelamount of last time or deviation between an intake manifold pressure ofa present time and an intake manifold pressure of last time with asecond reference adaptation parameter and a second correction factor.10. The fuel injection amount control system for an internal combustionengine according to claim 6, wherein in a compensation term for thefirst-order lag element B, a second wall adhesion correction amount isobtained by multiplying a deviation between a required fuel amount of apresent time and a required fuel amount of last time or deviationbetween an intake manifold pressure of a present time and an intakemanifold pressure of last time with a second reference adaptationparameter and a second correction factor.
 11. The fuel injection amountcontrol system for an internal combustion engine according to claim 7,wherein in a compensation term for a first-order lag element B, a secondwall adhesion correction amount is obtained by multiplying a deviationbetween a required fuel amount of a present time and a required fuelamount of last time or deviation between an intake manifold pressure ofa present time and an intake manifold pressure of last time with asecond reference adaptation parameter and a second correction factor.12. The fuel injection amount control system for an internal combustionengine according to claim 8, wherein in a compensation term for afirst-order lag element B, a second wall adhesion correction amount isobtained by multiplying a deviation between a required fuel amount ofthis time and a required fuel amount of last time or deviation betweenan intake manifold pressure of this time and an intake manifold pressureof last time with a second reference adaptation parameter and a secondcorrection factor.